1. Field of the Invention
The present invention relates to electric motors, more particularly, to switched reluctance motors.
2. Description of the Related Art
Electric motors, along with power electronics technologies, play an important role in the development of Electric Vehicles (EV). In EV applications, electric motors are desired to have a high starting torque for initial acceleration, high torque density and high efficiency to extend battery life. Consequently, design of an electric motor for EV has to address to the above needs.
Recent advances in power electronic technologies have made Switched Reluctance Motor (SRM) an attractive candidate for Electric Vehicle (EV) due to advantages such as simple and rugged motor construction, low weight, low manufacturing cost, easy cooling, excellent power-speed characteristics, high torque density, high operating efficiency, inherent fault tolerance, direct-drive, high transmission efficiency, highly reliable and simple drive train system.
SRM is an electromagnetic motor that is capable of producing high torque at low speed, making it a good candidate for direct driving purposes. Its torque is produced by the tendency of its moveable part to move to a position where the inductance of the excited winding is maximized. In addition, SRM has a simple and firm construction with no windings or permanent magnets in the rotor. Due to the geometrical simplicity of SRM, it has a lower cost of manufacturing and maintenance than other types of electric motors, and its reliability and robustness appear to be improved. Furthermore, the driving power converter of SRM has an independent circuit for each phase, which provides the great advantages of inherent fault tolerance and the potential of high reliability.
FIG. 1 illustrates a conventional four-phase switched reluctance motor (SRM) 100 that includes a ring-like outer stator 101 having 8 stator poles, and an inner rotor 104 having 6 poles outwardly extended, and a shaft 103 fixed to the rotor 104. Each of the stator poles includes a coil winding 102. To obtain the rotational motion from the rotor 104, a stator phase (i.e., a pair of diametrically opposed stator poles) is excited, through supply of electric current, when rotor 104 is moving from an unaligned position towards an aligned position, and likewise, moving from an aligned position towards an unaligned position. In this regards, through sequential excitation of the stator phases, a continuous motoring motion can be performed in a clockwise or counterclockwise direction.
However, since the rotor of a conventional SRM is located inside of the stator, the rotation of the rotor cannot directly lead to the rotational of a wheel when it is used in an in-wheel design. Thus, a specially designed in-wheel SRM is needed.